1. Field of the Invention
The present invention relates to a semiconductor device, particularly to a semiconductor device having a capacitor.
2. Description of the Related Art
In recent years, development of a ferroelectric memory (FeRAM: Ferroelectric Random Access Memory) in which a ferroelectric film is used as a dielectric film of a capacitor has been advanced. Examples of a typical ferroelectric film for use in the ferroelectric memory include a Pb(ZrxTi1-x)O3 film (PZT film) and SrBi2Ta2O9 film (SBT film).
With the use of metal oxide films such as the PZT film and SBT film in the dielectric film, there is a problem that the metal oxide film is reduced by hydrogen in plasma process such as a CVD process and RIE process performed after forming the capacitor. As a result, spontaneous polarization of a ferroelectric material deteriorates. In this manner, characteristics and reliability of the capacitor deteriorate.
Moreover, in a ferroelectric memory, heat treatment at a high temperature in an oxygen atmosphere is required in order to recover the damage generated in the capacitor in the plasma process. However, there is a problem that a plug is oxidized by such heat treatment in the ferroelectric memory having a capacitor-on-plug structure (COP) in which the plug is disposed right under the capacitor. As a result, electric connection of the capacitor to the plug becomes insufficient, and the characteristics and reliability of the ferroelectric memory deteriorate.
To solve the above-described problem, it is necessary to cover the capacitor with a protective insulating film which has hydrogen and oxygen barrier properties. However, when the capacitor is formed and thereafter the protective insulating film is deposited, it is difficult to obtain satisfactory step coverage. Therefore, there is a problem that the barrier properties are insufficient.
In U.S. Pat. No. 6,153,460, there is proposed a method of forming a bottom electrode of the capacitor by a CMP process. For example, after forming a hole in an insulating film including a silicon oxide film and titanium oxide film, the hole is filled with a bottom electrode film by the CMP process. With the use of the CMP process in this manner, it is possible to solve the above-described step coverage problem. However, it can hardly be said that the silicon oxide film and titanium oxide film used as the insulating film have satisfactory barrier properties. Therefore, it is difficult to avoid the above-described problems of oxidation and reduction of the dielectric film.
As described above, in the prior-art manufacturing method, it is difficult to secure the hydrogen barrier property and oxygen barrier property, and therefore there is a problem that the characteristics and reliability of the semiconductor device having the capacitor deteriorate.